The present invention relates to an information reproducing method and an information reproducing device, in particular to an information reproducing method and an information reproducing device that can perform adaptive equalization of digital signals reproduced from an information recording medium with favorable equalization properties without sacrificing information storage capacities.
When digital signals are reproduced from information recording media, such as optical disks, waveform equalization is used for the suppression of interference between symbols, which can negatively affect the symbol error rate, and for the realization of partial response technology, which improves the symbol error rate by generating a specified interference between symbols.
Because property variations of the transmission path are caused by the slightly varying properties of each information recording medium, adaptive equalization technology is used, which updates the equalization properties of the waveform equalizer to adapt to the changes of the transmission path properties.
An example of adaptive equalization technology, which is explained in the prior art section of Publication of Unexamined Japanese Patent Application No. H9-7031, is a technique in which a special learning region is provided on the information recording medium, the learning region is reproduced before the reproduction of the data region, and the generation of the reproduction clock and adaptive learning processing are performed using the resulting signal.
FIG. 12 shows an optical disk reproducing device employing this conventional adaptive equalization technology. Moreover, FIG. 13 shows the sector configuration of the optical disk in FIG. 12.
The sector 1010 shown in FIG. 13 is a recording unit when digital information is to be recorded on an information recording medium, and consists of an address portion 1001 and a data portion 1002.
The address portion 1001 indicates the physical location of the sector 1010, and is prerecorded at the time the optical disk is manufactured.
The data portion 1002 is the region where the user records information, and includes a VFO region 1003, an adaptive learning region 1004, and a data region 1005.
The VFO region 1003 is a continuous data pattern that is provided to precisely generate the reproduction clock necessary at the time of signal reproduction, and the reproduction clock generator 130 in FIG. 12 generates the reproduction clock using the reproduction signal from this pattern.
FIG. 14 shows the configuration of the reproduction clock generator. As shown in FIG. 14, a comparator 131 compares the reproduction signal with a predetermined slice level, and detects its zero crossing point. A VCO 134 oscillates at a frequency proportional to the input voltage, and is the oscillator for outputting the reproduction clock signal. A phase comparator 132 compares the timing of the zero crossing of the reproduction signal with the timing of the edge of the reproduction clock signal outputted by VCO 134, and outputs a pulse whose width is proportional to the phase error determined by the phase comparator. A low-pass filter (LPF) 133 lets only low frequency components outputted by the phase comparator 132 pass, and feeds this output to the VCO 134.
With this configuration, a reproduction clock can be generated that depends on the variations of the disk""s rotation speed, because when the output voltage of the phase comparator 132 changes in accordance with the phase difference, the VCO 134 changes its oscillator frequency accordingly.
In the adaptive learning region 1004, a known bit pattern is recorded for performing an adaptation learning process, which updates the equalization properties of the waveform equalizer 107. The equalization error is determined by determining the difference between the digital reproduction signal attained by reproducing this bit pattern and an equalization target value uniquely set for each bit pattern. Adaptive learning processing is performed by determining, in an adaptation algorithm, the equalization property values of the waveform equalizer 107 minimizing this equalization error.
With an optical disk having such a sector configuration, the optical disk reproducing device in FIG. 12 first of all accesses the sector 1010, in accordance with the information recorded in the address portion 1001.
If the access to the target sector 1010 is successful, the VFO region 1003 is reproduced by the optical head 103, the reproduction clock generator 130 generates the reproduction clock based on this reproduced signal, and the reproduction clock is then fed to various parts of the optical disk reproducing device.
Then, the optical head 103 reproduces the adaptive learning region 1004, and this reproduced signal is A/D converted in synchronization with the regeneration clock, thereby obtaining the digital reproduction signal. The obtained digital reproduction signal is fed to the waveform equalizer 107 and the adaptive learning device 108.
The waveform equalizer 107 performs waveform equalization, and the adaptive learning device 108 adjusts the waveform equalizer 107 to appropriate equalization properties by performing adaptive learning processing.
After the adaptive learning is finished, the data region 1005 is reproduced, and after the waveform has been equalized with the waveform equalizer 107, it is demodulated with a demodulator 111.
With this processing, it is possible to synchronize the reproduction time of the data region constantly with the reproduction clock, and to perform waveform equalization with equalization properties commensurate with the properties of the transmission path.
However, in the adaptive equalization processing with this conventional information reproducing device, VFO regions and adaptive learning regions, which cannot store user data, have to be provided to obtain good reproduction properties. As a result, some of the limited data capacity of the information recording medium has to be sacrificed.
To avoid sacrificing data capacity, methods without adaptive learning regions have been proposed, which determine a prediction equalization error by presupposing the reproduction signal with a certain threshold as a reference, and perform an adaptive learning operation to reduce this prediction equalization error. But with this structure, the performance of the adaptive learning is worse than if known data on the adaptive learning region are reproduced to determine a precise equalization error.
In particular, in the initial stage of the adaptive learning, there is no guarantee that the equalization properties of the waveform equalizer are suited to the transmission path of the circuit. In such a case, the prediction equalization error is wrong, and as a result, the convergence speed of the adaptive learning decreases, and in the worst case may even diverge.
Moreover, in the case of an information reproduction medium such as an optical disk reproducing device, when defocussing or variations of the disk reflectivity, or level variations in the reproduction signal waveform due to power variations of the laser occur, then the position of the zero crossing point output by the comparator 131 strays from its initial position, and the VCO 134 cannot generate a precise reproduction clock.
When no precise reproduction clock can be supplied, the timing of the sampling of the reproduction signal performed by the A/D converter 106 in FIG. 12 becomes off, and the signal level of the digital reproduction signal obtained as the output of the A/D converter 106 varies. As a result, the properties of the adaptive learning process performed with the digital reproduction signal deteriorate, and it becomes difficult to perform suitable waveform equalization.
Moreover, in the adaptive learning processing with a conventional information reproducing device, the reproduction signals from the adaptive learning region all are used for adaptive learning, but when the signal level of the reproduction signal strays widely from an equalization target value due to, for example, defects on the surface of the information recording medium, the resulting equalization error itself is wrong, and it becomes impossible to determine the correct equalization property value.
It is an object of the present invention to solve the above-noted problems of the prior art, and to provide an information reproduction method and an information reproducing device that can perform adaptive equalization processing with constantly good equalization properties, without sacrificing data capacity.
To achieve this object, a first information reproduction method of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises storing a reproduction signal in a memory and waveform-equalizing the reproduction signal with a first waveform equalizer; performing an adaptive learning operation, in which an adaptive learning device renews equalization properties of the first waveform equalizer with an adaptation algorithm; after the adaptive learning operation with the first waveform equalizer, setting the equalization properties of a second waveform equalizer to the equalization properties of the first waveform equalizer; reading out a signal from the memory and waveform-equalizing the signal with the second waveform equalizer; and demodulating the output of the second waveform equalizer with a demodulator. With this first information reproduction method, digital reproduction signals are stored temporarily in the memory, while adaptive learning is performed with the reproduction signal from the data region, and after suitable equalization property values have been determined by the adaptive learning, the data stored in the memory is read out and waveform-equalized, so that it becomes possible to perform waveform equalization of reproduction signals with constantly good equalization properties, even without providing special learning regions on the information storage medium.
In the first information reproduction method of the present invention, it is preferable that the second waveform equalizer is the first waveform equalizer, having terminated the adaptive learning operation. With this configuration, it is possible to perform waveform equalization of reproduction signals with constantly good equalization properties, without providing a plurality of waveform equalizers and without providing special learning regions on the information storage medium.
Moreover, in the first information reproduction method of the present invention, it is preferable that the memory is a FIFO memory. With this configuration, it becomes possible to read out the temporarily stored digital reproduction signals with a simple structure.
Moreover, in the first information reproduction method of the present invention, it is preferable that the information recording medium has a sector structure, and when the adaptive learning operation begins, the first waveform equalizer is set to predetermined equalization properties. With this configuration, the adaptive learning operation can be begun from suitable initial conditions depending on the reproduced sector position, and it becomes possible to reduce the possibility of a reproduction failure. Furthermore, in this case, it is preferable that the first waveform equalizer is set to equalization properties different from preceding equalization properties if a sector is reproduced where a reproduction error has occurred at the preceding reproduction time. With this configuration, it becomes possible to reduce the possibility of a reproduction failure.
Moreover, it is preferable that the first information reproduction method of the present invention further comprises using, as the information recording medium, an information recording medium on which clock pits are prerecorded that are used for deriving a reproduction clock; outputting a clock pit detection signal by detecting the clock pits from the reproduction signal with a clock pit detector; generating a reproduction clock with a reproduction clock generator from the clock pit detection signal; performing the adaptive learning operation, in which the adaptive learning device renews equalization properties of the first waveform equalizer with an adaptation algorithm, in synchronization with the reproduction clock. With this configuration, superior adaptive learning results can be attained, even when there are level variations in the reproduction signal. Moreover, the VFO regions that used to be necessary in the prior art become unnecessary, and it becomes possible to increase the capacity of the user data.
Moreover, it is preferable that the first information reproduction method of the present invention further comprises detecting with a defect detector, from the reproduction signal, a signal portion reproducing a defect portion on a surface of the information recording medium and outputting a defect detection signal; and performing the adaptive learning operation with the adaptive learning device, renewing the equalization properties of the first waveform equalizer using an adaptation algorithm while changing an update amount of the equalization properties of the first waveform equalizer in accordance with the defect detection signal. With this configuration, influences of unsuitable reproduction signals from defect areas can be avoided or reduced, which makes it possible to perform a reliable adaptive learning operation.
Moreover, in the first information reproduction method of the present invention, it is preferable that the adaptive learning operation of renewing the equalization properties of the first waveform equalizer with the adaptive learning device is performed using an adaptation algorithm whose precision is higher than the precision of an input signal of the first waveform equalizer. With this configuration, it is possible to perform a reliable adaptive learning operation without bringing about a larger size of the device.
A second information reproduction method of the present invention for reproducing digital signals with a reproduction head from an information recording medium on which clock pits used for deriving a reproduction clock are prerecorded comprises detecting clock pits from a reproduction signal with a clock pit detector and outputting a clock pit detection signal; generating a reproduction clock from the clock pit detection signal with a reproduction clock generator; waveform-equalizing the reproduction signal with a waveform equalizer; performing an adaptive learning operation in which an adaptive learning device renews equalization properties of the waveform equalizer with an adaptation algorithm, in synchronization with the reproduction clock; and demodulating an output of the waveform equalizer with a demodulator. With this second information reproduction method, the problem that the precision of the reproduction clock is damaged by level variations of the reproduction signal can be avoided. Moreover, VFO regions become unnecessary, and the capacity of the user data can be increased.
A third information reproduction method for reproducing digital signals with a reproduction head from an information recording medium comprises waveform-equalizing a reproduction signal with a waveform equalizer; detecting with a defect detector, from the reproduction signal, a signal portion reproducing a defect portion on a surface of the information recording medium and outputting a defect detection signal; performing the adaptive learning operation with an adaptive learning device, renewing the equalization properties of the waveform equalizer using an adaptation algorithm while changing an update amount of the equalization properties in accordance with the defect detection signal; and demodulating an output of the waveform equalizer with a demodulator. With this third information reproduction method, even if during the adaptive learning processing unsuitable data such as reproduction signals from a defect area are input into the adaptive learning device, the influence of such signals can be ignored or made very small, so that it becomes possible to perform a reliable adaptive learning operation.
A fourth information reproduction method of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises waveform-equalizing a reproduction signal with a waveform equalizer; performing an adaptive learning operation of renewing the equalization properties of the waveform equalizer with an adaptive learning device, using an adaptation algorithm whose precision is higher than the precision of an input signal of the waveform equalizer; and demodulating an output of the waveform equalizer with a demodulator. With this fourth information reproduction method, high precision calculations are performed only inside the adaptive learning device performing the calculation processing of the adaptation algorithm, so that it is possible to perform a reliable adaptive learning operation without bringing about a larger size of the device.
A fifth information reproduction method of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises storing a reproduction signal in a memory and waveform-equalizing the reproduction signal with first waveform equalization properties; performing an adaptive learning operation in which the first waveform equalization properties are renewed with an adaptation algorithm; after the adaptive learning operation, setting second waveform equalization properties to the first waveform equalization properties; reading out the reproduction signal from the memory and waveform-equalizing it with the second waveform equalization properties; and demodulating the reproduction signal after it has been waveform-equalized with the second waveform equalization properties.
A first information reproducing device of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises a memory for storing a reproduction signal; a first waveform equalizer for waveform-equalizing the reproduction signal; an adaptive learning device for performing an adaptive learning operation of renewing equalization properties of the first waveform equalizer with an adaptation algorithm; a second waveform equalizer for waveform-equalizing a signal read out from the memory, after the adaptive learning operation has been performed for the first waveform equalizer, and the equalization properties of the first waveform equalizer have been set as the equalization properties of the second waveform equalizer; and a demodulator for demodulating an output of the second waveform equalizer.
In the first information reproducing device of the present invention, it is preferable that the second waveform equalizer is the first waveform equalizer, after it has terminated the adaptive learning operation.
Moreover, in the first information reproducing device of the present invention, it is preferable that the memory is a FIFO memory.
Moreover, in the first information reproducing device of the present invention, it is preferable that the first waveform equalizer is set to predetermined equalization properties when the adaptive learning operation begins. In this case, it is preferable that the information recording medium has a sector structure, and the first waveform equalizer is set to equalization properties that are different from preceding equalization properties when a sector is reproduced that has caused a reproduction error at the preceding reproduction time.
In the first information reproducing device of the present invention, it is preferable that clock pits used for deriving a reproduction clock are prerecorded on the information recording medium; the information reproducing device further comprising a clock pit detector for detecting the clock pits from a reproduction signal and outputting a clock pit detection signal, and a reproduction clock generator for generating a reproduction clock from the clock pit detection signal; and the adaptive learning device renews the equalization properties of the first waveform equalizer in synchronization with the reproduction clock, using an adaptation algorithm.
Furthermore, it is preferable that the first information reproducing device of the present invention further comprises a defect detector for detecting, from the reproduction signal, a signal portion reproducing a defect portion on a surface of the information recording medium and outputting a defect detection signal; that the adaptive learning operation is performed with the adaptive learning device, renewing the equalization properties of the first waveform equalizer using an adaptation algorithm; and that an update amount of the equalization properties is changed in accordance with the defect detection signal.
In the first information reproducing device of the present invention, it is preferable that, when the adaptive learning operation of renewing the equalization properties of the first waveform equalizer is performed with an adaptation algorithm, the calculation processes of the adaptation algorithm are performed with higher precision than the precision of an input signal of the first waveform equalizer.
A second information reproducing device of the present invention for reproducing digital signals with a reproduction head from an information recording medium on which clock pits used for deriving a reproduction clock are prerecorded comprises a clock pit detector for detecting the clock pits from a reproduction signal and outputting a clock pit detection signal; a reproduction clock generator for generating a reproduction clock from the clock pit detection signal; a waveform equalizer for waveform-equalizing the reproduction signal; an adaptive learning device for performing an adaptive learning operation of renewing equalization properties of the waveform equalizer with an adaptation algorithm, in synchronization with the reproduction clock; and a demodulator for demodulating an output of the waveform equalizer.
A third information reproducing device of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises a waveform equalizer for waveform-equalizing a reproduction signal; a defect detector for detecting, from the reproduction signal, a signal portion reproducing a defect portion on a surface of the information recording medium and outputting a defect detection signal; an adaptive learning device for performing an adaptive learning operation of renewing the equalization properties of the waveform equalizer using an adaptation algorithm and changing an update amount of the equalization properties in accordance with the defect detection signal; and a demodulator for demodulating an output of the waveform equalizer.
A fourth information reproducing device of the present invention for reproducing digital signals with a reproduction head from an information recording medium comprises a waveform equalizer for waveform-equalizing a reproduction signal; an adaptive learning device for performing an adaptive learning operation of renewing the equalization properties of the waveform equalizer using an adaptation algorithm, performing calculation processes of the adaptation algorithm with a precision that is higher than the precision of an input signal of the waveform equalizer; and a demodulator for demodulating an output of the waveform equalizer.